For radio communication system, one important interest now lies in how wide a geographical region a service can be provided to, that is, the width of coverage of a system. Radio waves used for radio communication spatially attenuate due to factors such as the distance of propagation, presence of obstacles, reflection, or scattering and thus, overcoming an influence of attenuation of radio waves is key to expanding coverage of the system.
One method of expanding coverage of a radio communication system is to relay a radio signal via a relay station, that is, to use relay communication. In relay communication, a relay station is positioned between two communication apparatuses that are incapable of (or have difficulty in) directly transmitting/receiving a radio signal to each other and a radio signal is relayed by the relay station. In LTE (Long Term Evolution)-Advanced, which is a next-generation cellular communication standard under consideration by 3GPP (Third Generation Partnership Project), for example, improvement of throughput at cell edges is proposed by making full use of relay communication by relay stations. Moreover, by using relay communication, a mesh network can be constructed through the formation of a mesh-like network.
Examples of technology related to relay communication include, for example, Patent Literature 1 and Patent Literature 2 below. In Patent Literature 1 below, a technology to check an increase in power consumption by a relay station by extracting and relaying a portion of a subcarrier signal contained in a multicarrier signal in the relay station is described. In Patent Literature 2 below, a technology to prevent interference between a transmission signal and a reception signal and to realize stable relay communication by using a different channel for transmission of a signal to a destination from a channel used for reception of a signal from a source is described.